Fatal Errors

I was getting a Fatal Error when trying to login to the dashboard and went it an corrected that from “if ( is_user_admin () )” to “if ( is_user_admin )”. Then I tried to log in again and got this error |
“Fatal error: Call to undefined function add_screen_option() in /home/fireba6/public_html/content/wp-admin/index.php on line 28”. However on line 28 this is what I see:

add_screen_option(‘layout_columns’, array(‘max’ => 4, ‘default’ => 1 ) );

Can someone help me out? I had not made any changes to the site and this suddenly started happening when I tried to log in.